common/json: add a helper for json to u16

As Rusty pointed out to me, the gossip protocol restricts cltvs to u16
so at least we'll use this helper for them.

common/json.c

@@ -90,6 +90,21 @@ bool json_to_number(const char *buffer, const jsmntok_t *tok,
 	return true;
 }
 
+bool json_to_u16(const char *buffer, const jsmntok_t *tok,
+                 short unsigned int *num)
+{
+	uint64_t u64;
+
+	if (!json_to_u64(buffer, tok, &u64))
+		return false;
+	*num = u64;
+
+	/* Just in case it doesn't fit. */
+	if (*num != u64)
+		return false;
+	return true;
+}
+
 bool json_to_int(const char *buffer, const jsmntok_t *tok, int *num)
 {
 	char *end;

common/json.h

@@ -36,6 +36,10 @@ bool json_to_number(const char *buffer, const jsmntok_t *tok,
 bool json_to_u64(const char *buffer, const jsmntok_t *tok,
 		 uint64_t *num);
 
+/* Extract number from this (may be a string, or a number literal) */
+bool json_to_u16(const char *buffer, const jsmntok_t *tok,
+                 uint16_t *num);
+
 /* Extract double from this (must be a number literal) */
 bool json_to_double(const char *buffer, const jsmntok_t *tok, double *num);
 

plugins/pay.c

@@ -820,8 +820,6 @@ static struct command_result *add_shadow_route(struct command *cmd,
 	const jsmntok_t *chan, *best = NULL;
 	size_t i;
 	u64 sample = 0;
-	/* FIXME: Use route_info's cltv_expiry_delta member instead */
-	u32 cltv_fuzz;
 	struct route_info *route = tal_arr(NULL, struct route_info, 1);
 
 	json_for_each_arr(i, chan, channels) {
@@ -835,9 +833,9 @@ static struct command_result *add_shadow_route(struct command *cmd,
 				continue;
 
 			/* Don't use if total would exceed 1/4 of our time allowance. */
-			json_to_number(buf, json_get_member(buf, chan, "delay"),
-			               &cltv_fuzz);
-			if ((pc->final_cltv + cltv_fuzz) * 4 > pc->maxdelay)
+			json_to_u16(buf, json_get_member(buf, chan, "delay"),
+			            &route[0].cltv_expiry_delta);
+			if ((pc->final_cltv + route[0].cltv_expiry_delta) * 4 > pc->maxdelay)
 				continue;
 
 			json_to_number(buf, json_get_member(buf, chan, "base_fee_millisatoshi"),
@@ -857,14 +855,14 @@ static struct command_result *add_shadow_route(struct command *cmd,
 		return start_pay_attempt(cmd, pc, "Initial attempt");
 	}
 
-	pc->final_cltv += cltv_fuzz;
+	pc->final_cltv += route[0].cltv_expiry_delta;
 	pc->shadow_dest = json_strdup(pc, buf,
 				      json_get_member(buf, best, "destination"));
 	route_msatoshi(&pc->msat, pc->msat, route, 1);
 	tal_append_fmt(&pc->ps->shadow,
 		       "Added %u cltv delay, %u base fee, and %u ppm fee "
 		       "for shadow to %s.",
-		       cltv_fuzz, route[0].fee_base_msat,
+		       route[0].cltv_expiry_delta, route[0].fee_base_msat,
 		       route[0].fee_proportional_millionths,
 		       pc->shadow_dest);
 	tal_free(route);